Discharge rate is a key parameter affecting the cycle life of lithium-ion batteries (LIB). Normally, lithium-ion batteries deteriorate more severely at a higher discharge rate. In this paper, we report that the cycle performance of LiNi0.8Co0.15Al0.05O2/graphite high-energy 2.8 Ah 18650 cells is abnormally worse at a 1.5 C discharge rate than at a 2.0 C discharge rate. Combining macromethods with micromethods, the capacity/rate performance, electrochemical impedance spectroscopy (EIS), and scanning electron microscope (SEM) morphology of the electrodes are systematically investigated. We have found that the impedance of the negative electrodes after 2.0 C aged is smaller than that after 1.5 C aged, through EIS analysis, and the discharge rate performance of the negative electrodes after 2.0 C aged is better than that after 1.5 C aged through coin cell analysis. In addition, some special microcracks in the negative electrodes of aged cells are observed through SEM analysis, which can accelerate the side reaction between active and electrolyte and form the thicker SEI which will hinder the Li+ insertion and cause resistance increase. In short, the LiNi0.8Co0.15Al0.05O2/graphite-based lithium-ion batteries show better cycle life at a 2.0 C discharge rate than at a 1.5 C discharge rate which indicates that the negative electrodes contribute more than the positive electrodes.

中文翻译：

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LiNi0.8Co0.15Al0.05O2/石墨高能 18650 电池在 1.5 C 下比 2.0 C 的劣化速度异常快

放电率是影响锂离子电池（LIB）循环寿命的关键参数。通常，锂离子电池在更高的放电率下劣化更严重。在本文中，我们报告了 LiNi0.8Co0.15Al0.05O2/石墨高能 2.8 Ah 18650 电池在 1.5 C 放电速率下的循环性能比在 2.0 C 放电速率下异常差。将宏观方法与微观方法相结合，系统地研究了电极的容量/倍率性能、电化学阻抗谱 (EIS) 和扫描电子显微镜 (SEM) 形态。我们通过EIS分析发现2.0C老化后负极的阻抗小于1.5C老化后的阻抗，2.0C老化后负极的放电倍率性能优于1.5C老化后的负极。通过纽扣电池分析老化 5 C。此外，通过SEM分析观察到老化电池负极存在一些特殊的微裂纹，这些微裂纹会加速活性物质和电解质之间的副反应，形成较厚的SEI，阻碍Li+的插入并导致电阻增加。简而言之，LiNi0.8Co0.15Al0.05O2/石墨基锂离子电池在2.0C放电倍率下比在1.5C放电倍率下表现出更好的循环寿命，这表明负极贡献大于正极。